In this study, we showed that the PR binding site within the ESR1 intronic sequence in T47D breast cancer cells exhibits the classical epigenetic marks found at active enhancer regions, including the monomethylation of lysine 4 of histone 3 (H3K4me1), a low DNA methylation and a DNase hypersensitivity [2,15]. This evidence concerns the gene ESR1 and breast cancer.